Database Languages
Two types of languages are there: 1. Data – Definition Language (DDL) 2. Data – Manipulation Language (DML) 1. Data – Definition Language (DDL) A Data – Definition Language specifies the database schema by set of definitions. For example, create table customer (cust_name char (20), cust_number integer , cust_address char (50), cust_city char (20), cust_pincode integer ) On executing the above DDL statement, the customer table is created and also updates special set of tables called the data dictionary or data directory . A data dictionary contains metadata , which is data about data. The example of the metadata is the schema of the table. Before modifying or reading actual data, the database system consults the data dictionary. The implementation details of the database schema, which are hidden from the users, are defined by the data storage and definition language statements. 2. Data – Manipulation Language (DML) The Data – Manipulation Language expresses datab